Touch screens are prevalent in today's computing environment. Portable computers, desktop computers, tablets, smart phones, and smartwatches may employ a touch screen to gain user input for navigation and control of these devices. Thus, discerning the intent of the user via touch inputs becomes an important feature of a touch screen device.
A touch from a single large finger can be problematic to conventional touch sensing techniques. For example, under weak ground conditions, the detected touch strength value profile of such a single large finger touch may appear as shown in the chart of FIG. 1, which is to say that it may appear as a region of touch strength values of relatively lower magnitude (reference A) surrounded by a region of touch strength values of relatively higher magnitude (reference B). In FIG. 1, a threshold touch strength value of 140 is used to determine whether a touch strength value is of a “lower” magnitude or if a “higher” magnitude. A strength value below the threshold touch strength value of 140 is a lower magnitude indicated by reference A, while a strength value above the threshold touch strength value of 140 is a higher magnitude indicated by reference B.
It is common for conventional touch sensing techniques to support detection of multiple touches. Finger separation algorithms are commonly applied to each touch data island (a group of interconnected nodes with strength values having a magnitude above certain threshold, as described above) so as to determine and analyze for multiple simultaneous touches. When such finger separation algorithms are applied on touch strength values such as that shown in FIG. 1, there is a chance that this data will be incorrectly interpreted as multiple touches by small fingers, instead of correctly interpreted as a single large finger.
Recognizing the commercial desirability of a method to distinguish a touch by a single large finger from multiple touches made by small fingers, and to stop a touch by a large finger from being incorrectly separated by the finger separation algorithms into multiple simultaneous touches, techniques for detecting a single touch by a large finger have been developed. However, while such techniques have been successful at distinguishing a single touch by a large finger from multiple touches by a small finger, they face challenges when multiple touches are made by large fingers, particularly along a same force or sense line of the touch screen. Such multiple touches by large fingers can lead to unwanted touch separation, touch breaks, ghost touches, or undesirable touch merges.
Therefore, further development into touch sensing techniques capable of not only distinguishing a single touch by a large finger from multiple touches made by smaller fingers, but also of accurately determining multiple touches from large fingers, is needed.